학술논문
Quasifree photoproduction of $\eta$ mesons off protons and neutrons
Document Type
Working Paper
Author
A2 Collaboration; Werthmüller, D.; Witthauer, L.; Keshelashvili, I.; Aguar-Bartolomé, P.; Ahrens, J.; Annand, J. R. M.; Arends, H. J.; Bantawa, K.; Beck, R.; Bekrenev, V.; Braghieri, A.; Branford, D.; Briscoe, W. J.; Brudvik, J.; Cherepnya, S.; Costanza, S.; Demissie, B.; Dieterle, M.; Downie, E. J.; Drexler, P.; Fil'kov, L. V.; Fix, A.; Glazier, D. I.; Hamilton, D.; Heid, E.; Hornidge, D.; Howdle, D.; Huber, G. M.; Jaegle, I.; Jahn, O.; Jude, T. C.; Käser, A.; Kashevarov, V. L.; Kondratiev, R.; Korolija, M.; Kruglov, S. P.; Krusche, B.; Kulbardis, A.; Lisin, V.; Livingston, K.; MacGregor, I. J. D.; Maghrbi, Y.; Mancell, J.; Manley, D. M.; Marinides, Z.; Martinez, M.; McGeorge, J. C.; McNicoll, E. F.; Metag, V.; Middleton, D. G.; Mushkarenkov, A.; Nefkens, B. M. K.; Nikolaev, A.; Novotny, R.; Oberle, M.; Ostrick, M.; Otte, P. B.; Oussena, B.; Pedroni, P.; Pheron, F.; Polonski, A.; Prakhov, S. N.; Robinson, J.; Rosner, G.; Rostomyan, T.; Schumann, S.; Sikora, M. H.; Sober, D.; Starostin, A.; Supek, I.; Thiel, M.; Thomas, A.; Unverzagt, M.; Watts, D. P.
Source
Phys. Rev. C 90, 015205 (2014)
Subject
Language
Abstract
Differential and total cross sections for the quasifree reactions $\gamma p\rightarrow\eta p$ and $\gamma n\rightarrow\eta n$ have been determined at the MAMI-C electron accelerator using a liquid deuterium target. Photons were produced via bremsstrahlung from the 1.5 GeV incident electron beam and energy-tagged with the Glasgow photon tagger. Decay photons of the neutral decay modes $\eta\rightarrow 2\gamma$ and $\eta\rightarrow 3\pi^0 \rightarrow 6\gamma$ and coincident recoil nucleons were detected in a combined setup of the Crystal Ball and the TAPS calorimeters. The $\eta$-production cross sections were measured in coincidence with recoil protons, recoil neutrons, and in an inclusive mode without a condition on recoil nucleons, which allowed a check of the internal consistency of the data. The effects from nuclear Fermi motion were removed by a kinematic reconstruction of the final-state invariant mass and possible nuclear effects on the quasifree cross section were investigated by a comparison of free and quasifree proton data. The results, which represent a significant improvement in statistical quality compared to previous measurements, agree with the known neutron-to-proton cross-section ratio in the peak of the $S_{11}(1535)$ resonance and confirm a peak in the neutron cross section, which is absent for the proton, at a center-of-mass energy $W = (1670\pm 5)$ MeV with an intrinsic width of $\Gamma\approx 30$ MeV.